As weight or resistance based strength training has become increasingly popular and more prevalent fitness activity, equipment used in strength training has progressed from simple free weights to stacked weight machines, spring resistance machines, and hydraulic or pneumatic resistance machines. In many strength training regimens hydraulic and/or pneumatic resistance equipment is preferred over free weights and other direct weight systems for a number of reasons, including safety.
Because hydraulic and pneumatic resistance training equipment not only reduces the risk of physical injury but also tends to smooth movements and bodily impact to the degree that such equipment is much more suitable to achieving a “low impact” exercise regime. Pneumatic equipment is more effective in providing a low impact workout than hydraulic, because of the inherent cushioning effect provided by the compressible gas as opposed to a non-compressible liquid such as hydraulic fluid. In addition, hydraulic and/or pneumatic equipment can be used to impose resistance to movement in both “push” and “pull” directions, so as to work two muscle groups with a single piece of equipment. It is also known that the hydraulic and/or pneumatic equipment can be adjusted to provide a different level of resistance for the push stroke and the pull stroke.
However, all hydraulic equipment and pneumatic equipment designs known in the prior art utilize relatively simple valve assemblies to increase and decrease resistance by respectively decreasing or increasing the area of the fluid flow passageway through the valve or valves. While this approach does allow some degree of adjustment in resistance, in reality the degree of control is limited by the fact that the resistance to movement in prior art systems is directly proportional to the speed of movement. The faster a user pushes or pulls against the resistance, the higher the resistance provided by the machine becomes, and conversely the slower the user pushes or pulls, the lower the resistance becomes. This disadvantage is most significant for users whose training objectives are best achieved by rapid movement or a combination of relatively rapid movements and relatively slow movements against a consistent resistance. For example, swimmers derive the most benefit from a combination of movements against a relatively low, but consistent resistance, whereas body builders benefit more from slower repetitions against a high, consistent resistance. Neither the hydraulic nor the pneumatic equipment known in the prior art is capable of providing consistent resistance independently of speed of movement, despite the clear need for such a system.